Building Stone Retaining Walls Tips DIY

Dry-stack vs. Mortared

• Stone retaining walls can be dry-stacked or mortared. Dry-stack walls rely on gravity, friction and the positioning of the stones for stability, while mortared walls are bound with cement or concrete, making the wall almost one solid unit. While it may seem as if mortared walls would be the best choice, dry-stacked walls are actually ideal for retaining walls because groundwater can freely flow through the cracks between stones. This relieves pressure on the wall so the pressure from the ground and groundwater doesn't push it over. Stones for a dry-stack wall must be carefully chosen and placed to create an interlocking structure; arrange the stones according to size so it's easier to find the stone needed to fit a particular space.

Height and Tilt

• Dry-stacked stone walls are most stable when they are 3 feet tall or shorter. In many areas, a stone wall more than 4 feet tall may require a building permit or professional installation. This doesn't mean that stone walls can only hold back hills up to 3 or 4 feet tall, however. A hill can host several short stone retaining walls with a leveled terrace stepped back onto the hill. Build a 3-foot-high retaining wall at the base, cut the hill back about 5 or 6 feet and then build another short retaining wall. Retaining walls must be built so they tilt against the hillside. As a general rule, the wall should tilt back 2 inches for every foot of wall height; a 3-foot-tall wall should have 6 inches of tilt.

Foundation and Backfill

• A major advantage of keeping retaining walls short is that walls up to 3 feet tall don't need a concrete footing and can be laid directly on soil, if desired. Dig a trench for the wall, and lay the stones in the trench to anchor the stone wall to the soil. Some builders prefer to lay a base of leveled, compacted gravel in the trench for a firm foundation. If gravel is used, add the depth of the gravel to the 6-inch measurement so the stones are still anchored. When the wall is built, longer bond stones should be placed at every third or fourth level to protrude from the back of the structure. The bond stones work as anchors to bond the wall to the backfill; crushed rock or gravel backfill should be poured between the wall and hillside after you've laid three or four courses of stone.

Capping

• Capping a stone retaining wall helps to hold everything together and should be the last step of the project after building and backfilling the wall. The wall can be capped with stone, if desired. Mortar should be applied to the top of the wall and the cap stones. Lay large, flat stones on top of the wall, running in the opposite direction from the rest of the stones in the wall. For a completely mortar-free wall, the retaining wall can be capped with plants. In this method, building is stopped 6 to 8 inches from the top, and the area is filled with soil to bring it to the desired grade. Plant ground cover in the soil; the roots help bind the wall and prevent erosion.